The present invention relates to a new system of detection of entanglements of warp threads across a shed that closes the shed to the passage of a shuttle in a multi-phase weaving textile loom. This new system, being endowed with characteristics of differential sensitivity, and of memorization of the signalling of the entanglement position, secures an efficacious and optimum operation of the loom, with its immediate stopping only in strictly necessary cases.
It is known that the hindrances or obstacles which the shuttle can meet during its run through the shed (formed by the warp threads in a multi-step loom) are of three types, viz., namely, unstable entanglements of weakly entangled threads, weak but persistent entanglements which are not loosened by the shuttle passage, and strong entanglements.
A system of detection of a closed shed, for supplying an optimum performance, should hence be able to filter the above said faults. Such a system should not stop the machine in the presence of unstable weak entanglements which are opened by the passage of the same shuttle, but signal the persistent entanglements stopping the loom, and stop the machine as immediately as possible in the presence of strong entanglements. Furthermore, the system should be also provided with a permanent memory of the signalling of persistent entanglements, for the purpose of securing the looming stoppage even if the instantaneous transmission of the stop signal is hindered by a particular and contingent arrangement of the warp threads.
From the prior art, different types of detection systems are already known, but none of these systems are able to fulfill the above-said requirements.
In fact, the known system of exploiting the increase in the resistance to the shuttle running caused by an obstacle present across the shed, such as, e.g., a strong entanglement of warp threads, has major drawbacks. This system reacts to a strong entanglement of warp threads by causing the shuttle to be more pressed against a sensitive control bar, which thus interrupts the electrical system of control of the loom and stops this latter. In addition to not enabling the operator to detect the possible weak persistent entanglements, with the consequent production of faulty fabrics, this prior art system has the drawback that, due to the natural delay in loom stopping relative to the entanglement presence signal, the shuttle continues to press against the obstacle present inside the shed, with the possibility that the warp thread mey get broken before the loom is stopped.
Another system of the prior art, consisting in providing a side wall of the shuttle with a sensitive control elastic blade controlling the tranducers which supply the loom stopping signal has the drawback of a delayed action in that, when the blade detects the presence of an obstacle, the shuttle has already penetrated, by a large portion of its length, into the defect, possibly causing the fabric under way of formation to be irretrievably damaged. Furthermore, the adjustment of the stiffness of said elastic blade is very difficult to gauge in that it is requested to fulfill opposite needs, viz., it should be not too sensitive, so to be able to loosen the unstable entanglements without stopping the loom. And it should be, at the same time, very sensitive, so to be able to signal the persistent entanglements.
In practice, an intermediate stiffness is adopted, so that often useless stops of the loom occur, because of the (not too low) sensitivity of the blade.
Finally, none of the known systems is provided with a memory of the stop signal.